This invention relates to a programmed welding machine with a weld head speed override.
The invention is an improvement over certain concepts disclosed in my co-pending U.S. patent application Ser. No. 24,696, filed Mar. 28, 1979, entitled "Programmed Welding Machine with Continuously Monitored Override Control", and assigned to a common assignee.
Welding machines which have a programming device associated therewith for directing the welding head along a predetermined path have long been in use. The programming device may include apparati as numerical control (N/C), templates with tracer followers and the like. The welding machines have been used to manufacture large parts such as booms, c-frames, vehicle lift arms, etc., which may include not only straight line segments but also contoured segments.
In the manufacture of large parts such as those mentioned above, they have often been formed from an assembly of two or more individual pieces which have been initially created by flame cutting them with plasma or like torches from a large workpiece. The individual pieces are then tack welded if desired and fixedly positioned adjacent each other to form a groove or seam. A welding head is then moved along the groove to apply a bead which joins the pieces together.
In addition, contouring devices are already known which include a transverse beam or bridge which defines a transverse or X axis and which is movable along rails or the like which define a longitudinal or Y axis. A carriage mounted for movement along the bridge carries a metal working tool, such as a cutting torch or the like.
Furthermore, it is known to mount a sensing means such as a probe adjacent a welding head for the purpose of sensing the position of the edge of a groove or seam for welding, and to broadly provide a slide mechanism for adjusting the position of the welding head in accordance with the positional output of the probe.
In the above-identified co-pending patent application, a welding machine is provided wherein main horizontal X and Y axes are defined. A mounting device is carried beneath the carriage of the welding machine, for mounting an assembly comprising a welding head and a weld groove sensor. This mounting device comprises a rotator which defines a vertical C axis about which the tips of the welding head and sensor can be rotated.
A programming device, such as a numerical control arrangement or a tracer, is programmed in the usual manner to move the machine parts, and thus the welding head and sensor assembly, relative to the main X and Y axes, and may be used to turn the rotator so that the said assembly turns about the C axis. Programmed turning of the assembly is for the purpose of maintaining the sensor in a position ahead of the welding head along the welding groove, no matter what the contour thereof. A feedback from the main drive motors for the machine and rotator satisfies the programming device that the welding head and sensor assembly is where it is programmed to be.
In the device of the said co-pending patent application, the programming device is overridden in a manner so that the welding head is continuously moved from the programmed path to a desired corrected path defined by deviations in the weld groove, without affecting the program.
A slide assembly is connected between the machine carriage and the welding head and sensor assembly, with the slide assembly defining a plurality of axes of deviation, such as X.sub.d and Y.sub.d. The slide assembly is adapted to be driven by motors, one for each axis of deviation, to cause translation of the welding head from its programmed path to the desired deviated path in accordance with the deviation in the weld groove.
For purposes of control of the slide motors, the shaft of a sine-cosine resolver is gearingly connected in a one-to-one relationship to a gear forming part of the rotator. The stator windings of the resolver are connected to the slide motors and are responsive to a voltage fed to the resolver rotor or shaft winding. The stator winding signal is responsive to the deviated position of the sensor in the weld groove relative to the programmed weld head position and, depending upon the amount of deviation, drives the slide motors to provide a correction in the welding head position.
The rotary position of the resolver shaft, and thus the rotor winding, relative to the stator windings, provides a setting of the resolver which determines the ratio of the relative corrective drive signals to be fed to the slide motors. The resolver shaft's rotary position is, in turn, responsive to the rotary position of the rotator, through the gearing connection.
As the welding machine is operated, the programming device drives the welding head along a straight or contoured path relative to the main X and Y axes, which is the generally desired path for forming the weld in a groove between two pieces to be joined. At the same time, the programming device may turn the rotator when necessary about the vertical C axis to maintain the sensor ahead of the welding head. Deviations from the programmed path in a direction perpendicular thereto are sensed by the sensor which, through the resolver, instructs the slide motors to move the welding head from its programmed path and along the X.sub.d and/or Y.sub.d axes to the actual desired deviated path.
Although the welding head is caused to deviate from its programmed path when needed, the programming device is unaffected thereby and may be used to weld other identical pieces which may have different deviations.
The embodiment of the device disclosed in the said co-pending patent application is adapted to join one pair of members into a single intergral unit along a weld seam. Said device also utilizes a resolver with a one-phase rotor and two-phase stator.
For purposes of increasing production, it would be desirable to weld a plurality of pairs of members so that more than one identical integral unit may be produced at the same time on the same machine. Generally, this could be accomplished by placing a plurality of weld heads on the transverse bridge, together with duplicate X.sub.d Y.sub.d slides and controls, and by programming the weld path identically for each weld head. If a plurality of similar pairs of tack welded workpieces were positioned on the horizontal table, the weld heads would then join these pairs simultaneously.
The concept of multiple joining is subject to a major difficulty due to the fact that the gap width to be seam welded may vary from pair to pair. This is due to the fact that the preparatory tack welds, as well as the workpiece edges, will not be identical for each pair, because of tolerance variations.
In multiple seam welding, if the same respective portions of the various seam are identical in width, the machine can be programmed to provide identical weld head speeds which will lay down beads of proper width for the width of the gaps. These beads will all be the same. However, if the gaps are of different widths, and with the same speed as previously, the situation changes. A gap may be narrower than normal so that too much weld bead is laid down. Or, a gap may be wider than normal so that not enough weld bead is laid down. If one gap is too wide, while at the same time another is too narrow, it may be narrow, it may be necessary to set the machine speed for the narrow gap, thus creating an inadequate fill for the wide gap, and then doing a second special pass to fully fill the wide gap.
Attempts to vary the relative speeds of the bridge and/or carriage during an operating cycle to compensate for deviations of gap widths may pose substantial operational difficulties.
It is a task of the present invention to make it possible to simultaneously weld seams of varying width on the same machine without requiring multiple passes or complex relative speed adjustments between the bridge and carriage.
It is a further task to take advantage of the presence of an X.sub.d Y.sub.d deviation correction control on a programmed welding machine to produce welds of high quality even when the gap widths vary from normal or from each other.
It is yet another task of the invention to utilize the said deviation correction control regardless of whether or not there is a deviation present and independent of the program.
Broadly, the inventive concept is directed to providing a relatively simple means for varying the operating speed of one or more of a plurality of weld heads in a selective manner and separate from the speed control for the bridge and/or carriage.
In accordance with one aspect of the invention, a device is provided to cause the X.sub.d slide and/or the Y.sub.d slide in a weld head mount of the type disclosed in the aforementioned patent application to selectively change the effective speed of a weld head along the seam in accordance with the particular gap width to be welded.
In accordance with another aspect of the invention, the rotor of the resolver in the deviation correction control of the type disclosed in the said patent application, is of the two-phase type, with one of the rotor windings being selectively controllable to impress a signal on the X.sub.d and/or Y.sub.d slide drive motors, independent of the program or the existence of any deviation, to move the weld head relative to the carriage, and thus change its effective speed. The selectively controllable rotor winding is disposed at 90.degree. to the other rotor winding which is utilized in the deviation correction control.
In accordance with another aspect of the invention, when a deviation does occur, the deviation correction rotor winding and the speed variation rotor winding provide signals that are summed to drive the slide motors.
The various aspects of the invention are adapted to be incorporated into each weld head of a multi-seam welding machine.